To be honest, I CAN see the OP's point.
My best friend is a gay surgery resident in a program that is located in a large, traditionally liberal city.
He doesn't tell people that he's gay, and he doesn't come across as being obviously gay, either. He knew that he might have a few problems being in a traditionally conservative field, but I think it still aggravates him nonetheless.
He's heard people throw around gay jokes in his presence, and ask him, "You're not a ***, right? Thank God!". (He's also gotten that question, with significantly more vulgar words in place of "***.") His worst experience, though, was being scrubbed into a long case with a scrub tech who (with good intentions) kept badgering him to go on a date with her niece.
Would all this stop if he were openly gay? Maybe....maybe not. I don't think he's particularly anxious to find out, though. The last thing he needs (or wants) as a resident is to be hassled for his sexual orientation.
Is this the case everywhere? No, almost definitely not. Do I understand the OP's concerns? Sure, absolutely.